This invention relates to improvements in and concerning a plastic ball valve.
Concerning improvements in a plastic ball valve, the applicant of the present patent application formerly applied for a utility model registration on a construction of the plastic ball valve comprising a ball possessed of a trapezoidal groove, a stem possessed of a trapezoidal protuberance conforming to said trapezoidal groove, a handle fitted with an elastic metal piece coupled with a notch formed in said stem, and carriers contacted with said ball and connected via intervening O rings with body caps as illustrated in FIG. 3.
The ball valve of the prior invention covered by Japanese Utility Model Application No. 69896/1972 has a construction such that the positions of the carriers cannot be fixed at the stage of assembly. It is, therefore, not very easy for the ball valve to be assembled by having the ball kept at the center. In this construction, the stress due to the thermal expansion of the pipe is exerted directly upon the ball via the carriers. with the result that the handle torque is increased and the wear of the seat is accelerated to degade the sealing property of the valve. If the center of the pipe and the axis of the flow path in the valve fall to coincide with each other and yet the pipe is forcibly connected to the valve body, then the pipe is slanted with respect to the union bodies. Consequently, the force with which the carriers are held in contact with the ball is partially increased, the magnitude of the handle torque is increased and the contact between the valve body and the carriers via the intervening O rings becomes deficient to the extent of suffering leakage through the cap nuts while the handle is completely opened. This forms an inevitable defect of this ball valve.